This invention relates to blends of carbonate polymers with monovinyl aromatic polymers and, in particular, those blends which are highly impact resistant.
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers appear suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance, excellent electrical properties, glass-like transparency and good clarity are required.
Unfortunately, however, these polymers are expensive in price and require a high amount of energy expenditure in extrusion and molding processes. In order to reduce the cost of processing carbonate polymers, said polymers may contain other polymeric additives that reduce costs and lower the temperatures required for molding processes. Although such polymeric additives act to lower the melt viscosity of essentially pure polycarbonate, and thus reduce processing costs, such additives generally cause the mixture to become translucent and exhibit a lower impact resistance.
More recently, for example, as taught in U.S. Pat. No. 3,239,582, alkenylaromatic resins may be blended and injection molded with polycarbonate resins. While said resins, when blended in small amounts, do not have a substantial deleterious effect on the physical properties of the polycarbonate, they do introduce deleterious effects at high concentrations of additive relative to the polycarbonate. In order to significantly reduce the cost of the carbonate polymer blend, it is desirable to employ relatively large amounts of additives without adversely affecting many of the desirable physical and mechanical properties of the polycarbonate.
In view of the deficiencies of conventional carbonate polymer compositions, it would be highly desirable to provide an economical composition exhibiting improved processability and, optimally, having good transparency and clarity while maintaining good toughness even when relatively large amounts of polymeric additive are present in the blend.